The invention concerns a method of applying mortar to the underside of a building block to be laid, and an apparatus for carrying out that method.
The term building block is used broadly to denote blocks, bricks and the like of varying sizes and configurations, which are to be laid in various structures for building purposes.
In laying brickwork it is still the usual practice for the mortar, in particular for the bed joints, to be applied by hand to the top side of the brickwork which has already been erected, and then for the next layer of building blocks or bricks to be put on to the mortar bed prepared in that way. That is also the case when for example so-called flat blocks produced from porous concrete are laid by means of thin-bed mortar, which is frequently also referred to as the `bonding agent`.
The procedure involving applying and distributing the mortar or thin-bed mortar, which hitherto usually precedes laying the next layer of building blocks, requires a high degree of experience and skill in order to overcome a whole series of difficulties.
Thus for example a relatively accurately controlled amount of mortar has to be put on to the top side of the brickwork and distributed with a very high degree of uniformity over a portion whose length greatly depends on the conditions prevailing at that time. If for example mortar with a relatively low water content is distributed over an excessively long length of brickwork which at that time is exposed to strong sunlight, then during the period of time. that is required for the subsequent operation of laying the next layer of building blocks, the mortar in the portion in which the last blocks are to be laid may already have dried to such an extent that there is no longer any guarantee of producing a proper bonding effect and the old material has to be scraped out and replaced by fresh mortar. A corresponding consideration also applies when using mortar at temperatures of below 0.degree. C., at which an excessively long period of time between the step of applying the mortar and laying a building block thereon can result in the mortar freezing.
The layer of mortar which is applied first is also urged apart in the horizontal direction by virtue of the weight of the building block laid thereon and the pressing force which is to be exerted in order to make the bed joint of uniform thickness. If an excessive amount of mortar was applied, the result is that the mortar material comes out of the bed joints and runs down on the brickwork surfaces, and that makes it necessary to carry out a subsequent cleaning operation. If too little mortar was applied, there is no guarantee of a proper bonding action.
If the building blocks to be laid do not have a closed top side or if their abutting surfaces have irregular gaps or engagement recesses which are intended to permit the building block to be gripped by means of gripping cradles, a relatively large amount of material drops into those vertical gaps when mortar is applied manually so that the consumption of mortar is unnecessarily high unless the procedure is conducted with a high degree of care. The latter however involves an increased amount of time, even for a skilled bricklayer.
In order to obviate those difficulties, in particular in regard to the consumption of mortar, a method of applying mortar to building blocks has therefore already been proposed (German laid-open application (DE-OS) No 42 26 795) in which the building block is fitted on its surface which in the brickwork forms the underside, on to a so-called metering grid and jointly with same pressed against the surface of the supply of mortar which is made ready in a tank or vat. In that case, mortar material passes through the open meshes of the metering grid and remains adhering to the underside of the building block. The metering grid is intended to ensure in that case that the layer of mortar adhering to the building block is of approximately uniform thickness which, when the building block is put on to the brickwork which has already been erected, is rendered further uniform by virtue of the fact that the mortar material is distributed into the surface regions of the underside of the building block, which were initially not covered with mortar because of the shielding effect of the bars of the metering grid.
As with that known method the amount of mortar adhering to the underside of the building block is very heavily dependent both on the surface nature of the building block and also on the consistency of the mortar, and as those parameters can vary greatly from one case to another, the thickness of the layer of mortar which is actually achieved is still substantially dependent on the skill of the operator using the known apparatus, and in particular the force with which the operator presses the metering grid with building block disposed thereon, against the surface of the supply of mortar. That pressing force cannot be adapted to a given situation by a one-off adjustment, but has to be kept within relatively narrow limits afresh in each individual pressing operation. The step of individually putting the building blocks on to the metering grid and the operation of pressing that unit against the surface of the supply of mortar, under a defined force, is also a procedure which consumes a relatively large amount of time.